Nurses plan to strike at 6 a.m. Thursday. The hospital has spent $4 million to hire temporary replacement nurses, who will work for five days, beginning Thursday.

"We are disappointed by management's refusal to negotiate a settlement to this contract, yet we are committed to standing up for patients and our union rights," said Margaret McLaughlin, a nurse and co-chairwoman of the University Campus bargaining unit, in a statement.

Nurses who work at the Memorial and Hahnemann campuses reached a contract agreement last week and agreed not to strike.

The sticking point at University Campus is about staffing levels, especially at night, according to the Massachusetts Nurses Association. Nurses want the hospital to set a patient-to-nurse ratio of 5-to-1. "Right now it's 7-to-1 and sometimes 8-to-1," said David Schildmeier, spokesman for the association.

Nurses and hospital administrator also disagree on pensions, vacation time and other issues.

UMass Memorial Health Care President and CEO Eric Dickson said in a statement late Monday that the University Campus bargaining unit came in with a proposal that “far exceeded the agreed-upon terms” of the Memorial-Hahnemann package accepted on Friday.

“As the Medical Center has repeatedly informed the MNA, it has already incurred significant costs to prepare for the threatened strike,” Dr. Dickson said. “Nevertheless, the MNA’s demands would force us to incur even greater costs to avert the ill-considered strike.”

He said the medical center will not agree to a package that is “unfair or inequitable with the contract terms that nearly 1,000” nurses in the Memorial-Hahnemann bargaining unit agreed to last week.

No other negotiating sessions are scheduled before the strike, according to Mr. Schildmeier.

UMass Memorial is telling patients that University Campus will be "fully operational" during the strike, but it is postponing some procedures scheduled for Thursday and Friday. Hospital spokesman Robert Brogna declined to say what procedures or how many will be delayed.

Patients staying at the hospital will be notified directly about the strike. UMass Memorial will also hang posters and distribute information cards to tell hospital visitors about the strike.

"The excellent quality of care that patients have come to expect from the Medical Center will continue without interruption no matter what," Mr. Brogna said by email.

The nurses' union and hospital administrators have been negotiating for more than a year. The talks became so tense that nurses last month authorized a one-day strike of protest. But UMass Memorial said it was contractually obligated to pay replacement nurses for a minimum of five days and will use the replacements for all five days.

A federal mediator aided with negotiations on Monday.

The state Department of Public Health plans to dispatch surveyors to the hospital during the strike to ensure patients receive safe, high-quality care.

But patients familiar with the hospital will notice a difference. Karen M. Ardinger of Leominster, who went to University Campus for 35 radiation treatments, said the strike will affect patients like her who are used to seeing the same nurses every day.

"You get to know them," she said. "They get to know you. They know your history."

The strike also will be felt by other hospital employees. Susan L. Kozicz, a non-union nurse practitioner, said she will have to report to work two hours early on Thursday, at 5 a.m.

"Patients will be well cared for," she said, but added, "I'm sure there will be anxiety. ... It's stressful for everyone involved."

University Campus includes UMass Memorial's emergency department and treats patients with severe and complicated conditions that community hospitals typically don't treat. UMass Memorial said the replacement nurses it hired, through a staffing agency, have experience working in similar environments.

Meanwhile, St. Vincent Hospital is watching what happens at UMass Memorial.

"In the event of a strike, St. Vincent Hospital will meet the needs of the community to the best of our ability," President and Chief Executive Erik G. Wexler said in a statement. "We will follow our procedures just as we would in any other situation that could cause a sudden influx of patients."